1. Field of the Invention
This invention relates to a method and apparatus for determining the work output of a rotary or piston, external or inernal combustion engine and is directed more particularly to a method and apparatus for multiplying cylinder pressure by changes in the volume of the cylinder with respect to changes in angle of the crankshaft.
2. Description of the Prior Art
One of the earliest methods of measuring IMEP was by directly recording on paper a pressure-volume (P-V) diagram by using various mechanical linkages which connect a recording pen to a piston of the engine and pressure measuring devices. The resulting P-V diagram was then cut out and the enclosed area determined. Later developments included the use of mechanical planimeters for measuring this area, the development of electronic volume transducers, the use of oscilloscope to display the P-V diagram in real time, and the use of cameras to record the P-V diagram for analysis. More recently, high speed digital recorders and computor analysis have been utilized.
Despite the sophistication of such recorders and computers, all the prior art methods involve post-run data reduction to determine the work output of an engine. With the present day research programs on engine efficiency, fuel economy, pollutant reduction and overall performance analysis there is a need for a method and apparatus to measure the IMEP of an engine in real time. Prior art patents for measuring IMEP include those such as U.S. Pat. No. 3,283,569 to King et al. The instrument disclosed uses the parameter dV/dt in its computation and measures only average IMEP. The measured value is an approximation, being limited to the fundamental plus the second harmonic. A separate volume transducer and dV/dt transducer are required for each cylinder in order to do simultaneous studies of IMEP for more than one cylinder.
U.S. Pat. No. 3,815,410 to William L. Brown, Jr. et al discloses apparatus for measuring IMEP by utilizing dV/dt which would introduce a phase error related to RPM. The phase correction provided is valid only at one frequency and one RPM and only if the volume signal is a pure sinusoid.